The present invention relates to the sphere of high-pressure pipes intended to equip an oil drilling and/or production installation. More precisely, it relates to an application of the hooping technique for reinforcing metal tubes by means of composite reinforcing elements.
The hooping technique consists in winding a reinforcing element, generally in form of a fiber band coated with a polymer, around a metallic core in order to increase the resistance of the core to the internal pressure without increasing its weight significantly, considering the low weight of the bands.
The core can be a metal tube, for example made of steel. The reinforcing element is an elongate element. It can have the shape of a strip, of a wire, or preferably of a series of wires or wick coated with a polymer matrix.
The reinforcing element can be wound around the core while introducing a tension therein. Thus, the reinforcing element wound around the core is subjected to a tensile stress, which causes the metallic core to be stressed. The prestress undergone by the core is similar to the prestress that would be produced by an outside collapse pressure.
Oil is produced from an offshore reservoir using a pipe generally referred to as riser, which allows the wellhead installed at the sea bottom to be connected to the surface. The riser is an extension of the tubing carrying the oil from the well bottom to the wellhead. The riser is provided with at least two auxiliary lines called kill line and choke line, whose main function is to establish a hydraulic connection between the sea surface and the wellhead at the sea bottom. More particularly, the auxiliary lines allow to supply the well with fluid by circulating below the closed blowout preventer, and/or to discharge a fluid from the well without passing through the inside of the riser which is not high pressure resistant. The fluid conveyed, resulting from an influx in an underground reservoir, can circulate at a pressure of 700 bars.
The present invention proposes using hooped tubes so as to reduce the weight of the auxiliary lines. Its aim is to provide a simple and economical embodiment of a high-pressure pipe element made of a hooped tube.
The present invention relates to a high-pressure pipe element comprising at least one hooping layer on a metallic core. The core consists of a main part to which two connection means are welded at each end. The main part comprises a number of hooping layers inducing a determined prestress in the core, and the pipe comprises additional hooping layers in a zone stretching on either side of the two welds.
According to the present invention, the additional hooping layers can stretch over at least 50 mm of the main part.
The ends of the connection means may not be hooped and can have a sufficient thickness to withstand at least the same internal pressure as the hooped main part.
The outer surface of the connection means can form a cone between the main part and each end of the connection means. The cones can be covered at least partly by the additional hooping means.
According to the present invention, the pipe element is coated over the total outer surface thereof with a protective layer made of glass fiber embedded in a coloured polyamide matrix.
The pipe element according to the present invention can be used to make an auxiliary line of a drilling riser, and the auxiliary line can be a kill line, a choke line, a booster line or a mud return line.